Research on the Detection Model and Method for Evaluating Spot Welding Quality Based on Ultrasonic A-Scan Analysis

Abstract

To establish a system which can judge the spot welding quality automatically and effectively, the mathematical and acoustic simulation models of the spot welds detection through ultrasonic A-scan are established. The following results can be obtained: (1) The quantitative relationship between nugget diameter and detecting oscillogram is deduced and verified by simulation and experiments, and then the nugget diameter mathematic model is developed. (2) The attenuation characteristic of ultrasonic waves in spot welds is studied. It shows that ultrasonic attenuation is caused by two reasons: one is absorptive and scattering effect determined by base metal, the other is the multiple reflection and transmission effect caused by the sheet-structure. And their contribution varies in different welds (no weld, undersize weld and good weld). (3) The assessment software of spot welding quality is developed, the weld nugget diameter, attenuation coefficient and spot welding quality can be obtained within a short time. In addition, the whole detecting process and system is designed. The research results of this paper indicate the feasibility of applying this spot welding quality detecting method to the automatic production line.